Stainless Steel Coil Tube for Fan Coil Unit Heat Exchangers
Product Overview
The Stainless Steel Coil Tube (盘管Coiltube), manufactured by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered tubing product specifically designed for integration into fan coil unit (FCU) heat exchanger assemblies. This product represents a critical component in modern HVAC (Heating, Ventilation, and Air Conditioning) systems, where thermal efficiency, corrosion resistance, and long-term operational reliability are paramount. The coil tube is formed into serpentine or spiral configurations that maximize heat transfer surface area within compact spatial envelopes, making it ideal for distributed air handling applications in commercial, residential, and industrial environments.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, primarily conforming to the following material grades:
- 304 Stainless Steel (AISI 304 / 1.4301): Contains approximately 18% Chromium (Cr) and 8% Nickel (Ni), offering excellent general-purpose corrosion resistance and formability.
- 316 Stainless Steel (AISI 316 / 1.4401): Enhanced with 2–3% Molybdenum (Mo), providing superior resistance to pitting and crevice corrosion, particularly in chloride-containing environments.
- 321 Stainless Steel (AISI 321 / 1.4541): Tantalum-stabilized grade suitable for elevated-temperature applications, with resistance to intergranular corrosion.
Key material properties include:
- Thermal Conductivity: 16.3 W/(m·K) at 20°C (304 grade), ensuring efficient heat exchange performance.
- Specific Heat Capacity: 0.50 kJ/(kg·K)
- Density: 7.93 g/cm³ (304 grade)
- Maximum Operating Temperature: 870°C (304 grade); 870°C (316 grade)
- Tensile Strength: ≥520 MPa (annealed condition)
- Yield Strength: ≥205 MPa (0.2% offset)
- Elongation: ≥40% (minimum)
Specifications
| Parameter | Specification |
|---|---|
| Product Category | Stainless Steel Coil Tube (盘管Coiltube) |
| Material Grade | AISI 304 / 316 / 321 (ASTM A213/A269) |
| Tube Outer Diameter (OD) | Φ6.0 mm – Φ12.7 mm (standard range) |
| Tube Wall Thickness | 0.3 mm – 1.0 mm |
| Tube Length (per coil) | 3.0 m – 12.0 m (customizable) |
| Coil Pitch (Serpentine) | 12 mm – 25 mm (adjustable per design) |
| Coil Diameter (Loop) | 30 mm – 80 mm |
| Surface Finish | Bright Annealed (BA) / Polished / Passivated |
| End Forming | Plain / Flared / Rolled / Welded Headers |
| Operating Pressure | Up to 1.6 MPa (working); 2.4 MPa (hydrostatic test) |
| Operating Fluids | Water / Glycol-Water Mixture / Refrigerant |
| Standards Compliance | ASTM A213 / ASME SA213 / GB/T 14976 / EN 10217 |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd. |
Manufacturing Process
The production of stainless steel coil tubes for fan coil unit heat exchangers follows a rigorous multi-stage manufacturing process:
- Raw Material Selection & Inspection: Cold-rolled stainless steel strip or seamless tube stock is sourced from certified mills, undergoing incoming quality inspection (IQI) for chemical composition, mechanical properties, and surface quality.
- Precision Forming (Seamless or Welded): Tubes are produced via cold-rolling and welding (ERW – Electric Resistance Welding) or seamless piercing methods, ensuring uniform wall thickness and dimensional accuracy.
- Heat Treatment (Solution Annealing): Tubes undergo solution annealing at 1050–1100°C followed by controlled cooling to restore full austenitic microstructure, relieve residual stresses, and ensure maximum corrosion resistance.
- Coil Forming & Bending: Using CNC-controlled coiling and bending machinery, the straight tube is formed into precise serpentine, spiral, or helical coil configurations with consistent pitch, radius, and alignment. Bend radii are maintained at a minimum of 3× tube OD to prevent wall thinning or ovalization.
- Header Welding & Assembly: Coil ends are welded to inlet/outlet headers (typically copper or stainless steel), using TIG (Tungsten Inert Gas) welding with argon back-purging to ensure penetration and prevent oxidation at the weld zone.
- Surface Treatment & Passivation: The finished coil tube undergoes pickling and passivation treatment to remove scale, contaminants, and free iron, establishing a protective chromium oxide layer for enhanced corrosion resistance.
- Pressure Testing & Quality Assurance: Each coil tube assembly undergoes 100% hydrostatic pressure testing at 1.5× working pressure, leak detection, and dimensional verification per applicable standards.
Applications
The stainless steel coil tube is integral to the following application domains:
- Fan Coil Units (FCU): Primary application — the coil tube serves as the core heat exchange element in both chilled water and hot water FCUs, facilitating sensible and latent heat transfer between air and fluid.
- Commercial HVAC Systems: Office buildings, hotels, hospitals, shopping malls, and educational facilities requiring distributed air conditioning.
- Residential Climate Control: Concealed and exposed FCU installations in high-end residential developments.
- Industrial Process Cooling/Heating: Temperature regulation in manufacturing facilities, data centers, and cleanrooms.
- Food & Beverage Industry: Hygienic-grade coil tubes (316L) for process heating and cooling where sanitary requirements are stringent.
- Marine & Coastal Applications: 316-grade coil tubes providing resistance to saltwater and humid coastal atmospheres.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management systems and certifications:
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health and Safety Management
- CE Marking — European Conformity for pressure equipment (PED 2014/68/EU)
- GB/T 14976 — Chinese National Standard for seamless stainless steel tubes
- Mill Test Certificates (MTC) — EN 10204 Type 3.1 for each batch
- NACE MR0175 — Compliance for sour service applications (where applicable)
Unique Selling Points
1. Superior Corrosion Resistance: Unlike traditional copper coil tubes, the stainless steel construction provides immunity to galvanic corrosion when paired with copper fins, eliminating a common failure mode in FCU heat exchangers.
2. Extended Service Life: The austenitic stainless steel matrix resists scaling, bio-fouling, and chemical attack from treated water systems, delivering a design life exceeding 25 years under normal operating conditions.
3. Precision Coil Geometry: CNC-controlled forming ensures uniform coil pitch and alignment, promoting balanced flow distribution and optimal heat transfer coefficients (U-values) across the entire heat exchanger face.
4. Hygienic Surface Quality: Bright annealed and passivated surfaces minimize bacterial adhesion, making these coil tubes suitable for pharmaceutical, food processing, and healthcare applications.
5. Environmental Sustainability: Stainless steel is 100% recyclable with no degradation of properties, aligning with global ESG (Environmental, Social, and Governance) sustainability goals.
6. Custom Engineering Capability: Wenzhou Jixing offers bespoke coil configurations — including variable pitch, multi-row arrangements, and custom header designs — tailored to specific thermal load requirements and spatial constraints.
Technical Reference
This product specification is informed by the analytical study documented in "Analysis of Heat Exchangers in Fan Coil Unit Assemblies" (风机盘管机组换热器的分析), which evaluates the thermodynamic performance, pressure drop characteristics, and long-term degradation mechanisms of coil tube configurations in FCU systems. The findings underscore the critical role of coil tube material selection, geometry optimization, and surface condition in achieving peak seasonal energy efficiency ratios (SEER) and coefficient of performance (COP) values.